The idea (and this is not our idea, this is how your Mac works) for having a strong distinction between active and inactive states is so that you can more easily tell where keyboard focus is. If there is little to no difference then you must struggle more to figure out what’s going to happen when you press ⌘delete. Is it going to delete some text to the beginning of the current line, delete the selected bookmark from the inspector (which uses the same visual signalling) or is it going to fire off the document to the Trash?
You do have some say in the matter though, in Appearance: Binder: Options, with Base selection color on background color. The selection and active document highlight will now no longer be based on your system defaults, and by tweaking the background colour of the binder itself, you can find areas where the algorithm creates more accentuation (or less, if that is what you want).
The “Solarized (Light)” theme, for example, makes it pretty obvious when the binder is focussed or not, but maybe the passive highlight is too subtle for you? “A Midsummer Night” on the other hand has almost no distinction between active and passive, and which is selected by Reveal is always very obvious.
And of course, you may also find that leaving the setting off, using system highlights, but a custom binder background is the better choice for you. Since system highlights do not change depending on the background colour, you can more easily find complimentary colours that offer very little ambiguity against inactive grey vs active accent colour.